Crosslinked siloxane outmost layer having aromatic siliconcontaining compounds for photoreceptors

ABSTRACT

An aromatic silicon-containing compound has the formula: 
 
Ar—[X-L-SiR n (OR′) 3-n ] m  
where Ar represents an aromatic group, X represents a divalent or trivalent group; L represents a divalent linking group; R represents a hydrogen atom, an alkyl group or an aryl group; R′ represents an alkyl group having 1 to 5 carbon atoms; n is an integer of from 0 to 2; and m is an integer of from 1 to 5. The aromatic silicon-containing compound can be used in electrophotographic photoreceptors, particularly in outmost protective layers of such electrophotographic photoreceptors.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to aromatic silicon-containing compounds,and to their use in silicon-containing outmost protective layers such asfor electrophotographic photoreceptors, and process cartridges and imageforming apparatuses containing photoreceptors having such protectivelayers. The present invention relates to methods of making such aromaticsilicon-containing compounds, crosslinked siloxane outmost protectivelayers, electrophotographic photoreceptors, process cartridges, andimage forming apparatuses.

2. Description of Related Art

In xerography, or electrophotographic printing/copying, acharge-retentive device called a photoreceptor is electrostaticallycharged. For optimal image production, the photoreceptor should beuniformly charged across its entire surface. The photoreceptor is thenexposed to a light pattern of an input image to selectively dischargethe surface of the photoreceptor in accordance with the image. Theresulting pattern of charged and discharged areas on the photoreceptorforms an electrostatic charge pattern (i.e., a latent image) conformingto the input image. The latent image is developed by contacting it withfinely divided electrostatically attractable powder called toner. Toneris held on the image areas by electrostatic force. The toner image maythen be transferred to a substrate or support member, and the image isthen affixed to the substrate or support member by a fusing process toform a permanent image thereon. After transfer, excess toner left on thephotoreceptor is cleaned from its surface, and residual charge is erasedfrom the photoreceptor.

Electrophotographic photoreceptors can be provided in a number of forms.For example, the photoreceptors can be a homogeneous layer of a singlematerial, such as vitreous selenium, or it can be a composite layercontaining a photoconductive layer and another material. In addition,the photoreceptor can be layered. Current layered photoreceptorsgenerally have at least a flexible substrate support layer and twoactive layers. These active layers generally include a charge generatinglayer containing a light absorbing material, and a charge transportlayer containing electron donor molecules. These layers can be in anyorder, and sometimes can be combined in a single or a mixed layer. Theflexible substrate support layer can be formed of a conductive material.Alternatively, a conductive layer can be formed on top of anonconductive flexible substrate support layer.

An electrostatographic photoreceptor can be in a rigid drumconfiguration or in a flexible belt configuration that can be either aseamless or a seamed belt. Typical electrophotographic photoreceptordrums comprise a charge transport layer and a charge generating layercoated over a rigid conducting substrate support drum. However, forflexible electrophotographic photoreceptor belts, the charge transportlayer and charge generating layer are coated on top of a flexiblesubstrate support layer. To ensure that the photoreceptor belts exhibitsufficient flatness, an anticurl backing layer can be coated onto theback side of the flexible substrate support layer to counteract upwardcurling and ensure photoreceptor flatness.

In many modern electrophotographic imaging systems the flexiblephotoreceptor belts are repeatedly cycled to achieve high speed imaging.As a result of this repetitive cycling, the outermost layer of thephotoreceptor experiences a high degree of frictional contact with othermachine subsystem components used to clean and/or prepare thephotoreceptor for imaging during each cycle. When repeatedly subjectedto cyclic mechanical interactions against the machine subsystemcomponents, photoreceptor belts can experience severe frictional wear atthe outermost organic photoreceptor layer surface that can greatlyreduce the useful life of the photoreceptor. Ultimately, the resultingwear impairs photoreceptor performance and thus image quality.

In order to mitigate erosion of the top outermost layer during theseprocesses, the outermost layer can be coated with a thin protectivelayer, such as a siloxane-containing or silicon hard overcoat asdisclosed in U.S. Patent Application Publication No. US 2004/0086794 A1,incorporated herein by reference in its entirety.

SUMMARY OF THE INVENTION

Applicants have discovered several shortcomings associated withcrosslinked siloxane-containing overcoat layers. In particular,Applicants have discovered that electrical charges can migrate from thephotoreceptor surface into the porous crosslinked siloxane-containingovercoat, and cause image problems. Furthermore, another shortcomingassociated with the siloxane-containing overcoat layers is the hightorque required to rotate the coated photoreceptor against a cleaningblade. In addition, because the silicon hard overcoat layers aretypically prepared by sol-gel processes, shrinkage of the applied layeroccurs, which strains the resulting materials. Although attempts havebeen made to solve these problems by modifying various componentmaterials, such modifications typically present trade-offs in terms ofimproving one property while deteriorating another property.

Accordingly, it is an object to provide an improved crosslinkedsiloxane-containing overcoat that improves the wear rate of thephotoreceptor without sacrificing electrographic performance. It isanother object of the invention to provide an improved matrix material,and methods of making such matrix material, that can be used incrosslinked siloxane-containing overcoat layers to provide the improvedresults.

Applicants have discovered that these and other problems can be overcomeby providing an aromatic silicon-containing compound, which can beincorporated into new crosslinked siloxane-containing outmost protectivelayers such as for use in electrophotographic photoreceptors. Such newaromatic silicon-containing compound provides such benefits as highrigidity and good compatibility with hole transport molecules typicallyused in crosslinked siloxane-containing overcoat layers. Crosslinkedsiloxane-containing protective layers and electrophotographicphotoreceptors formed using the aromatic silicon-containing compound inturn show improved micro-mechanical properties, such as low torque,higher wear resistance, and the like, and improved and sustainedperformance in deletion resistance.

In embodiments, the rigid aromatic matrix material is a silane compound,which is used as a matrix material in forming silicon hard overcoatlayers such as for use in electrophotographic photoreceptors. Inembodiments, the crosslinked siloxane-containing outmost layer comprisesa hole transport material, and the product of the hydrolysis andcondensation of an aromatic silicon-containing compound as a matrixmaterial. The crosslinked siloxane-containing outmost layer can alsocomprise one or more additional components, such as a polymeric binder,antioxidant, stabilizer, catalyst, solvent, and the like. In variousembodiments, the crosslinked siloxane-containing outmost layer comprisesthe product of the hydrolysis and condensation of the aromaticsilicon-containing compound added to the overcoat disclosed in U.S.Patent Application Publication No. US 2004/0086794 A1, the entiredisclosure of which is incorporated herein by reference in its entirety.

In embodiments, the photoreceptor comprises a charge generating layer, acharge transport layer, and a protective layer. The protective layercomprises a crosslinked siloxane-containing overcoat containing theproduct of the hydrolysis and condensation of an aromaticsilicon-containing compound.

In embodiments, the process cartridge comprises an electrophotographicphotoreceptor that includes, as a protective layer, a crosslinkedsiloxane-containing overcoat containing the product of the hydrolysisand condensation of an aromatic silicon-containing compound. In variousembodiments, the image forming apparatus comprises anelectrophotographic photoreceptor that includes, as a protective layer,a crosslinked siloxane-containing overcoat containing the product of thehydrolysis and condensation of an aromatic silicon-containing compound,at least one charging unit, at least one exposing unit, at least onedeveloping unit, a transfer unit, and a cleaning unit.

BRIEF DESCRIPTION OF THE DRAWINGS

Various exemplary embodiments of this invention will be described indetail, with reference to the following figures, wherein:

FIG. 1 is a block diagram outlining the elements of anelectrophotographic photoreceptor.

FIG. 2 is a schematic view showing a preferred embodiment of an imageforming apparatus of the invention.

FIG. 3 is a schematic view showing another preferred embodiment of animage forming apparatus of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A new aromatic silicon-containing compound is provided. The aromaticsilicon-containing compound can generally be an aromatic silanecompound, i.e., a compound having one or more silane groups separated bya linking group that is or contains one or more aromatic groups. Forexample, the aromatic silicon-containing compound can generally berepresented by the following formula (I):Ar-[X-L-SiR_(n)(OR′)_(3-n)]_(m)  (I).

In formula (I), Ar represents an aromatic group, which can have one ormore phenyl groups. Suitable examples of Ar include, but are not limitedto the following structures (II-1) to (II-44):

In formula (I), X represents a divalent/trivalent group. Suitableexamples of X include, but are not limited to: an oxy group (—O—), athio group (—S—), an oxycarbonyl group (—COO—), a thiocarbonyl group(—COS—), a carbamate group (—OCO—NH—), an imide group (—CO—N—OC—), anamide group (—CO—NH—), a carbonate group (—OCOO—) and the like, or adivalent group in which two or more of them are combined.

The typical examples of the aromatic silicon-containing compoundsinclude, but are not limited to:

In formula (I), L represents a divalent linking group. Suitable examplesof L include, but are not limited to: a divalent hydrocarbon grouprepresented by —C_(m)H_(2m)—, —C_(m)H_(2m-2)—, —C_(m)H_(2m-4)— (m is aninteger of 1 to about 15, and preferably from 2 to about 10), —CH₂—C₆H₄—or —C₆H₄—C₆H₄—, or a divalent group in which two or more of them arecombined. The divalent group may also optionally have a substituentgroup such as an alkyl group, a phenyl group, an alkoxyl group or anamino group on its side chain.

In formula (I), R represents a hydrogen atom, an alkyl group (preferablyan alkyl group having 1 to 10 carbon atoms) or an aryl group (preferablya substituted or unsubstituted aryl group having 6 to 15 carbon atoms).R′ represents an alkyl group (preferably an alkyl group having from 1 to5 carbon atoms.

In formula (I), n is an integer, which can be 0, 1 or 2, and m is aninteger, which can be from 1 to 10, preferably, from 1 to 5.

The aromatic silicon-containing compound can be prepared by any suitablemethod. For example, an exemplary process is a one-pot two-stepreaction, starting with the reaction of the starting materials with abase to form a salt of the starting compound, followed by reacting thesalt with a halo-alkylene-silane compound to provide the final product.For example, aromatic silicon-containing compound of the formula (I),where X represents —O— can be prepared by the following reaction:

Wherein Y represents a halogen group selected from a group consisting ofI, Br, Cl and F. This reaction process can be readily modified toprovide other desired aromatic silicon-containing compounds of formula(I).

More specifically, a phenol starting material is dissolved in analcoholic solvent. The resulting solution is mixed with a base such asan alkaline hydroxide and an alkaline alkoxide to form phenoxide salt.The salt is then mixed with a halo-alkylene-silane, such asiodoalkyldiisopropoxymethylsilane, bromoalkyldiisopropoxymethylsilane,and chloroalkyldiisopropoxymethylsilane in an aprotic solvent such asdimethylformamide (DMF). The temperature of the reaction is maintainedfrom about 25° C. to about 100° C., preferably, from about 50° C. toabout 90° C. The reaction is carried out for about 1 min to about 5hours, preferably from about 30 min to about 2 hours. After the reactionthe product can be isolated by any suitable method, such as solventextraction. The final product can be purified by any process known inthe art, such as distillation, recrystallization, and flash columnchromatography. The desired structures of products can be confirmed with¹H NMR spectroscopy.

In embodiments, the aromatic silicon-containing compound, such as thearomatic silicon-containing compound of formula (I) is hydrolyzed andcondensed to form a crosslinked siloxane-containing component, which isincorporated into the protective layer. The product of hydrolysis andcondensation of the aromatic silicon-containing compound can preferablybe present in an amount of about 5% to about 80% of the total weight ofcrosslinked siloxane-containing outmost protective layer. Preferably,the product of hydrolysis and condensation of the aromaticsilicon-containing compound, such as the aromatic silicon-containingcompound of formula (I), is present in an amount of about 20% to about60% of the total weight of the silicon hard overcoat layer.

The aromatic silicon-containing compound, such as the aromaticsilicon-containing compound of formula (I), can be advantageously usedto form a crosslinked siloxane-containing outmost protective layer, suchas for use in an electrophotographic photoreceptor. Such crosslinkedsiloxane-containing outmost protective layers are generally known in theart, and can generally include a hole transport material, a binderresin, and the aromatic silicon-containing compound of formula (I). Thecrosslinked siloxane-containing outmost protective layer can furtherinclude, if desired, an additional polymeric binder resin, anantioxidant, a catalyst, a solvent, and the like, in known amounts fortheir known purposes.

An advantage of the aromatic silicon-containing compounds is that theyprovide improved properties of the crosslinked siloxane-containingoutmost protective layer. For example, a root cause of image deletionproblems in conventional overcoat layers is believed to be thephenomenon that the hole transport molecule tends to aggregate in theprotective layer due to incompatibility of the hole transport materialwith the conventional aliphatic silicon binders. When this aggregationoccurs, the hole transport molecules tend to be oxidized to cause theimage deletion problem. Thus, in embodiments, it is preferred that thearomatic silicon-containing compounds are used in place of conventionalaliphatic silicon-containing compounds. Use of the aromaticsilicon-containing compounds also provides more uniform or homogeneousdistribution of the hole transport molecule in the crosslinkedsiloxane-containing outmost protective layer.

Furthermore, it is known that conventional crosslinkedsiloxane-containing overcoat layers are soft, rubbery materials thatcause high torque of the photoreceptor with a cleaning blade. However,the inventors discovered that use of the aromatic silicon-containingcompounds form rigid aromatic matrix materials that provide a harder andstiffer overcoat layer, which in turn reduces the torque of thephotoreceptor with the cleaning blade, and thereby provides improvedimage quality.

Micromechanical properties of the crosslinked siloxane-containingoutmost protective layers can be evaluated by nanoindentationmeasurement, indicating that the protective layers including the productof the hydrolysis and condensation of the aromatic silicon-containingcompounds of formula (I) show improved reduced elastic modulus andhardness as compared with the conventional crosslinkedsiloxane-containing overcoat containing the aliphatic silicon-containingcompounds. These properties are shown in the following Table 1. TABLE 1Silicon-containing compounds used in the protective layers ReducedElastic Hardness (see Examples below) Modulus (GPA) (MPA) aliphatic 3.00± 0.15 120 ± 5 I-1 3.31 ± 0.14  117 ± 10 I-2 3.56 ± 0.08 137 ± 9 I-53.43 ± 0.09 142 ± 5 I-6 3.77 ± 0.17 153 ± 6

In embodiments, the hole transport molecules are triarylamines. Morespecifically the hole transport molecules can be selected fromsilicon-containing hole transport compounds represented by the followinggeneral formula (III), as well as hydrolysate or hydrolytic condensatesthereof.W²(-D-SiR_(3-a)Q_(a))_(b)  (III)wherein W² represents an organic group derived from a compound havinghole transport capability, Q represents a hydrolytic group, D representsa divalent group, a represents an integer of 1 to 3, b represents aninteger of 2 to 4, and c represents an integer of 1 to 4.

R represents a hydrogen atom, an alkyl group such as an alkyl grouphaving 1 to 10 or 1 to 5 carbon atoms or a substituted or unsubstitutedaryl group, such as a substituted or unsubstituted aryl group having 6to 15 carbon atoms.

Further, the hydrolytic group represented by Q means a functional groupthat can form a siloxane bond (O—Si—O) by hydrolysis in the curingreaction of the compound in formula (III). Non-limiting examples ofhydrolytic groups that may be used in embodiments include a hydroxylgroup, an alkoxyl group, a methyl ethyl ketoxime group, a diethylaminogroup, an acetoxy group, a propenoxy group and a chloro group. Inparticular embodiments, a group represented by —OR″ (R″ represents analkyl group having 1 to 15 carbon atoms or a trimethylsilyl group) maybe used.

In formula (III), the divalent group represented by D may be, inembodiments, a divalent hydrocarbon group represented by —C_(n)H_(2n)—,—C_(n)H_(2n-2)—, —C_(n)H_(2n-4)— (n is an integer of 1 to about 15, andpreferably an integer of 2 to about 10), —CH₂—C₆H₄— or —C₆H₄—C₆H₄—, anoxycarbonyl group (—COO—), a thio group (—S—), an oxy group (—O—), anisocyano group (—N═CH—) or a divalent group in which two or more suchgroups are combined. The divalent group D may have a substituent groupsuch as an alkyl group, a phenyl group, an alkoxyl group or an aminogroup on its side chain. When D is one of the above-mentioned divalentgroups, proper flexibility may be imparted to an organic silicateskeleton, which improves the strength of the layer.

Further, in the above-mentioned formula (III), there is no particularlimitation on the organic group represented by W², as long as it is agroup having hole transport capability. However, in particularembodiments, W² may be an organic group represented by the followinggeneral formula (IV):

wherein Ar¹, Ar², Ar³ and Ar⁴, which may be the same or different, eachrepresents a substituted or unsubstituted aryl group, Ar⁵ represents asubstituted or unsubstituted aryl or arylene group, k represents 0 or 1,and at least one of Ar¹ to Ar⁵ may be connected with -D-SiR_(3-a)Q_(a)in general formula (III).

Ar¹ to Ar⁴ in the above-mentioned general formula (IV) are eachpreferably any one of the following formulas (V) and (VI):

In formulas (V) and (VI), R⁶ represents a member selected from the groupconsisting of a hydrogen atom, an alkyl group having 1 to 4 carbonatoms, an alkoxyl group having 1 to 4 carbon atoms, an unsubstitutedphenyl group or a phenyl group substituted by an alkoxyl group having 1to 4 carbon atoms, an aralkyl group having 7 to 10 carbon atoms, and ahalogen atom; Ar represents a substituted or unsubstituted arylenegroup; X represents -D-SiR_(3-a)Q_(a) in general formula (III); mrepresents 0 or 1; and t represents an integer of 1 to 3.

Here, Ar in formula (VI) may be one represented by the following formula(VII) or (VII):

In formulas (VII) and (VIII), R¹⁰ and R¹¹ each represent a memberselected from the group consisting of a hydrogen atom, an alkyl grouphaving 1 to 4 carbon atoms, an alkoxyl group having 1 to 4 carbon atoms,an unsubstituted phenyl group or a phenyl group substituted by analkoxyl group having 1 to 4 carbon atoms, an aralkyl group having 7 to10 carbon atoms, and a halogen atom; and t represents an integer of 1 to3.

Further, Z′ in formula (VI) is preferably one represented by any one ofthe following formulas (IX) to (XVI):

In formulas (XV) to (XVI), R¹² and R¹³ each represent a member selectedfrom the group consisting of a hydrogen atom, an alkyl group having 1 to4 carbon atoms, an alkoxyl group having 1 to 4 carbon atoms, anunsubstituted phenyl group or a phenyl group substituted by an alkoxylgroup having 1 to 4 carbon atoms, an aralkyl group having 7 to 10 carbonatoms, and a halogen atom; W represents a divalent group; q and r eachrepresents an integer of 1 to 10; and t represents an integer of 1 to 3.

W in the above-mentioned formulas (XV) and (XVI) may be any one ofdivalent groups represented by the following formulas (XVII) to (XXVI):

In formula (XXIV), u represents an integer of 0 to 3.

Further, in general formula (IV), Ar⁵ is the aryl group illustrated inthe description of Ar¹ to Ar⁴, when k is 0, and an arylene groupobtained by removing a certain hydrogen atom from such an aryl group,when k is 1.

Combinations of Ar¹, Ar², Ar³, Ar⁴, Ar⁵ and integer k in formula (IV)and a group represented by -D-SiR_(3-a)Q_(a) in general formula (III) inparticular exemplary embodiments are shown in Table 2; additionalexemplary embodiments can be found in US 2004/0086794 and U.S. Pat. No.6,730,448 B2, the entire disclosures of which are incorporated herein byreference. In Table 2, S represents -D-SiR_(3-a)Q_(a) linked to Ar¹ toAr⁵, Me represents a methyl group, Et represents an ethyl group, and Prrepresents a propyl group. TABLE 2 No. Ar¹ Ar² Ar³ & Ar⁴ Ar⁵ k —S V-1 

—

0 —(CH₂)₂—COO—(CH₂)₃—Si(O^(i)Pr)₃ V-2 

—

0 —(CH₂)₂—COO—(CH₂)₃—SiMe(O^(i)Pr)₂ V-3 

—

0 —(CH₂)₂—COO—(CH₂)₃—SiMe₂(O^(i)Pr) V-4 

—

0 —COO—(CH₂)₃—Si(O^(i)Pr)₃ V-5 

—

0 —(CH₂)₂—COO—(CH₂)₃—Si(O^(i)Pr)₃ V-6 

—

0 —(CH₂)₂—COO—(CH₂)₃—SiMe(O^(i)Pr)₂ V-7 

—

0 —(CH₂)₂—COO—(CH₂)₃—SiMe₂(O^(i)Pr) V-8 

—

0 —COO—(CH₂)₃—Si(O^(i)Pr)₃ V-9 

—

0 —(CH₂)₂—COO—(CH₂)₃—Si(O^(i)Pr)₃ V-10

—

0 —(CH₂)₂—COO—(CH₂)₃—SiMe(O^(i)Pr)₂ V-11

—

0 —(CH₂)₂—COO—(CH₂)₃—SiMe₂(O^(i)Pr) V-12

—

0 —COO—(CH₂)₃—Si(O^(i)Pr)₃ V-13

—

0 —(CH₂)₂—COO—(CH₂)₃—Si(O^(i)Pr)₃ V-14

—

0 —(CH₂)₂—COO—(CH₂)₃—SiMe(O^(i)Pr)₂ V-15

—

0 —(CH₂)₂—COO—(CH₂)₃—SiMe₂(O^(i)Pr) V-16

—

0 —COO—(CH₂)₃—Si(O^(i)Pr)₃

Further, in embodiments, the silicon overcoat may also include silanecoupling agents, such as a tetrafunctional alkoxysilane (c=4), such astetramethoxysilane or tetraethoxysilane; a trifunctional alkoxysilane(c=3), such as methyltrimethoxysilane, methyltriethoxysilane,ethyltrimethoxysilane, methyltrimethoxyethoxysilane,vinyltrimethoxysilane, vinyltriethoxysilane, phenyltrimethoxysilane,γ-glycidoxypropylmethyldiethoxysilane,γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyl-triethoxysilane,γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane,γ-aminopropylmethyldimethoxysilane,N-β-(aminoethyl)-γ-aminopropyltriethoxysilane,(tridecafluoro-1,1,2,2-tetrahydrooctyl)triethoxysilane,(3,3,3-trifluoropropyl) trimethoxysilane,3-(heptafluoroisopropoxy)propyltriethoxysilane,1H,1H,2H,2H-perfluoroalkyltriethoxysilane,1H,1H,2H,2H-perfluorodecyltriethoxysilane or 1H,1H,2H,2H-perfluorooctyltriethoxysilane; a bifunctional alkoxysilane(c=2), such as dimethyldimethoxysilane, diphenyldimethoxysilane ormethylphenyldimethoxysilane; and a monofunctional alkoxysilane (c=1),such as trimethylmethoxysilane.

In order to improve the strength of the photosensitive layer, thetrifunctional alkoxysilanes and the tetrafunctional alkoxysilanes may beused in embodiments, and in order to improve the flexibility andfilm-forming properties, the monofunctional alkoxysilanes and thebifunctional alkoxysilanes may be used in embodiments.

Silicone hard-coating agents containing such coupling agents can also beused in embodiments. Commercially available hard-coating agents includeKP-85, X-40-9740 and X-40-2239 (available from Shinetsu Silicone Co.,Ltd.), and AY42-440, AY42-441 and AY49-208 (available from Toray DowCorning Co., Ltd.).

In embodiments, non-silicon-containing hole transport molecules with theabove-mentioned generic formula (III) can also be used.

In embodiments, the polymeric binder resin used in the crosslinkedsiloxane-containing outmost protective layer is soluble in a liquidcomponent, and is selected depending on the kind of liquid component.For example, when the coating solution contains an alcoholic solvent(such as methanol, ethanol or butanol), a polyvinyl acetal resin such asa polyvinyl butyral resin, a polyvinyl formal resin or a partiallyacetalized polyvinyl acetal resin in which butyral is partially modifiedwith formal or acetoacetal, a polyamide resin, a cellulose resin such asethyl cellulose melamine-formaldehyde resin, and a phenol resin areavailable as the alcohol-soluble resins. These resins may be used eitheralone or as a combination of two or more of them. Of the above-mentionedresins, the polyvinyl acetal resin is preferred in terms of electriccharacteristics.

The weight-average molecular weight of the resin is preferably fromabout 2,000 to about 1,000,000, and more preferably from about 5,000 toabout 50,000. When the average molecular weight is less than 2,000, theeffect of enhancing discharge gas resistance, mechanical strength,scratch resistance, particle dispersibility, etc. tends to becomeinsufficient. On the other hand, when the average molecular weightexceeds 1,000,000, the solubility of the resin in the coating solutiondecreases, contributing to poor film formation.

Further, the amount of the resin soluble in the liquid component ispreferably from about 0.1 to about 20% by weight, and more preferablyfrom about 2 to about 15% by weight, based on the total amount of thecoating solution. When the amount added is less than 0.1% by weight, theeffect of enhancing discharge gas resistance, mechanical strength,scratch resistance, particle dispersibility, etc. becomes insufficient.On the other hand, exceeding 20% by weight results in an indistinctimage when the electrophotographic photoreceptor of the invention isused at high temperature and high humidity.

There is no particular limitation on the silicon-containing compoundused in the invention, as long as it has at least one silicon atom.However, a compound having two or more silicon atoms in its molecule ispreferably used. The use of the compound having two or more siliconatoms allows both the strength and image quality of theelectrophotographic photoreceptor to be achieved at higher levels.

In addition, a cyclic siloxane compound such ashexamethylcyclotrisiloxane (D3) and Octamethylcyclotetrasiloxane (D4)can be added into the crosslinked siloxane-containing outmost protectivelayer to provide lubricity to the photoreceptor surface.

In addition to the above components, various fine particles can also beadded to the crosslinked siloxane-containing outmost protective layer.The fine particles may be used either alone or as a combination of twoor more of them. Examples of the fine particles include fine particlescontaining silicon. The fine particles containing silicon are fineparticles containing silicon as a constituent element, and specificallyinclude colloidal silica and fine silicone particles. Other fineparticles include fine fluorine-based particles such as ethylenetetrafluoride, ethylene trifluoride, propylene hexafluoride, vinylfluoride and vinylidene fluoride, and semiconductive metal oxides suchas ZnO—Al₂O₃, SnO₂—Sb₂O₃, In₂O₃—SnO₂, ZnO—TiO₂, MgO—Al₂O₃, FeO—TiO₂,TiO₂, SnO₂, In₂O₃, ZnO and MgO.

In embodiments, one or more additives such as a plasticizer, a surfacemodifier, an antioxidant or an agent for preventing deterioration bylight can also be used in the crosslinked siloxane-containing outmostprotective layer. Acceptable plasticizers include, for example,biphenyl, biphenyl chloride, terphenyl, dibutyl phthalate, diethyleneglycol phthalate, dioctyl phthalate, triphenylphosphoric acid,methylnaphthalene, benzophenone, chlorinated paraffin, polypropylene,polystyrene and various fluorohydrocarbons.

In a first embodiment, the crosslinked siloxane-containing outmostprotective layer can be prepared by first mixing and reacting thearomatic silicon-containing compound of formula (I) with the holetransfer molecule, polymerizing the silanes to form oligomericsiloxanes, and then stabilizing the formed oligomeric siloxanes. Theresultant material may be mixed with other components, and formed intoan outmost protective layer, for example as disclosed in U.S. PatentApplication Publication No. US 2004/0086794 A1. In embodiments, thephotoreceptor is coated using a sol gel coating method to form thecrosslinked siloxane-containing outmost protective layer. Otherprocesses for forming the outmost protective layer and coatedphotoreceptors will be apparent based on the present disclosure.

Photoreceptor

The electrophotographic photoreceptor of the invention may be either afunction-separation type photoreceptor, in which a layer containing acharge generation substance (charge generation layer) and a layercontaining a charge transfer substance (charge transfer layer) areseparately provided, or a monolayer type photoreceptor in which both thecharge generation layer and the charge transfer layer are contained inthe same layer.

FIG. 1 is a cross-sectional view schematically showing an embodiment ofthe electrophotographic photoreceptor. The electrophotographicphotoreceptor 1 shown in FIG. 1 is a function-separation-typephotoreceptor in which a charge generation layer 13 and a chargetransfer layer 14 are separately provided. That is, an underlayer 12,the charge generation layer 13, the charge transfer layer 14 and aprotective layer 15 are laminated onto a conductive support 11 to form aphotosensitive layer 16. The protective layer 15 contains the siliconhard overcoat, i.e., contains a resin soluble in the liquid componentcontained in the coating solution used for formation of this layer andthe silicon compound.

The conductive support 11 includes, for example, a metal plate, a metaldrum or a metal belt using a metal such as aluminum, copper, zinc,stainless steel, chromium, nickel, molybdenum, vanadium, indium, gold ora platinum, or an alloy thereof; and paper or a plastic film or beltcoated, deposited or laminated with a conductive polymer, a conductivecompound such as indium oxide, a metal such as aluminum, palladium orgold, or an alloy thereof. Further, surface treatment such as anodicoxidation coating, hot water oxidation, chemical treatment, coloring ordiffused reflection treatment such as graining can also be applied to asurface of the support 11.

Binding resins used in the underlayer 12 include, specifically, apolyamide resin, a vinyl chloride resin, a vinyl acetate resin, a phenolresin, a polyurethane resin, a melamine resin, a benzoguanamine resin, apolyimide resin, a polyethylene resin, a polypropylene resin, apolycarbonate resin, an acrylic resin, a methacrylic resin, a vinylidenechloride resin, a polyvinyl acetal resin, a vinyl chloride-vinyl acetatecopolymer, a polyvinyl alcohol resin, a water-soluble polyester resin,nitrocellulose, casein, gelatin, polyglutamic acid, starch, starchacetate, amino starch, polyacrylic acid, polyacrylamide, a zirconiumchelate compound, a titanyl chelate compound, a titanyl alkoxidecompound, an organic titanyl compound and a silane coupling agent. Thesecan be used either alone or as a combination of two or more of them.Further, fine particles of titanium oxide, aluminum oxide, siliconoxide, zirconium oxide, barium titanate, a silicone resin or the likemay be added to the above-mentioned binding resin.

As a coating method in forming the underlayer, an ordinary method suchas blade coating, Mayer bar coating, spray coating, dip coating, beadcoating, air knife coating or curtain coating is employed. Inembodiments, the thickness of the underlayer is from 0.01 to 40 μm.

The charge generation substances contained in the charge generationlayer 13 include, for example, various organic pigments and organic dyessuch as an azo pigment, a quinoline pigment, a perylene pigment, anindigo pigment, a thioindigo pigment, a bisbenzimidazole pigment, aphthalocyanine pigment, a quinacridone pigment, a quinoline pigment, alake pigment, an azo lake pigment, an anthraquinone pigment, an oxazinepigment, a dioxazine pigment, a triphenylmethane pigment, an azuleniumdye, a squallum dye, a pyrylium dye, a triallylmethane dye, a xanthenedye, a thiazine dye and cyanine dye; and inorganic materials such asamorphous silicon, amorphous selenium, tellurium, a selenium-telluriumalloy, cadmium sulfide, antimony sulfide, zinc oxide and zinc sulfide.Of these, the cyclocondensed aromatic pigments, the perylene pigment andthe azo pigment are preferred in terms of sensitivity, electricstability and photochemical stability against irradiated light. Thesecharge generation substances may be used either alone or as acombination of two or more of them.

The charge generation layer 13 is formable by vacuum deposition of thecharge generation substance or application of a coating solution inwhich the charge generation substance is dispersed in an organic solventcontaining a binding resin. The binding resins used in the chargegeneration layer include a polyvinyl acetal resin such as a polyvinylbutyral resin, a polyvinyl formal resin or a partially acetalizedpolyvinyl acetal resin in which butyral is partially modified withformal or acetoacetal, a polyamide resin, a polyester resin, a modifiedether type polyester resin, a polycarbonate resin, an acrylic resin, apolyvinyl chloride resin, a polyvinylidene chloride, a polystyreneresin, a polyvinyl acetate resin, a vinyl chloride-vinyl acetatecopolymer, a silicone resin, a phenol resin, a phenoxy resin, a melamineresin, a benzoguanamine resin, a urea resin, a polyurethane resin, apoly-N-vinylcarbazole resin, a polyvinylanthracene resin and apolyvinylpyrene resin. These can be used either alone or as acombination of two or more of them.

Of these, when the polyvinyl acetal resin, the vinyl chloride-vinylacetate copolymer, the phenoxy resin or the modified ether typepolyester resin is used, the dispersibility of the charge generationsubstance is improved to cause no occurrence of coagulation of thecharge generation substance, thereby obtaining the coating solutionstable for a long period of time. The use of such a coating solutionmakes it possible to form a uniform coating easily and surely. As aresult, the electric characteristics are improved, thereby being able tosufficiently prevent the occurrence of an image defect. In embodiments,the compounding ratio of the charge generation substance to the bindingresin is within the range of 5:1 to 1:2 by volume ratio.

Further, the solvents used in preparing the coating solution includeorganic solvents such as methanol, ethanol, n-propanol, n-butanol,benzyl alcohol, methyl cellosolve, ethyl cellosolve, acetone, methylethyl ketone, cyclohexanone, chlorobenzene, methyl acetate, n-butylacetate, dioxane, tetrahydrofuran, methylene chloride and chloroform.These can be used either alone or as a mixture of two or more of them.

Methods for applying the coating solution include the coating methodsexemplified in the description of the above-mentioned underlayer.

Further, a stabilizer such as an antioxidant or an inactivating agentcan also be added to the charge generation layer 13. The antioxidantsinclude, for example, antioxidants such as phenolic, sulfur, phosphorusand amine compounds. The inactivating agents includebis(dithiobenzyl)nickel and nickel di-n-butylthiocarbamate.

The charge transfer layer 14 can be formed by applying a coatingsolution containing the charge transfer substance and a binding resin,and further fine particles, an additive, etc., as described above.

The low molecular weight charge transfer substances include, forexample, pyrene, carbazole, hydrazone, oxazole, oxadiazole, pyrazoline,arylamine, arylmethane, benzidine, thiazole, stilbene and butadienecompounds. Further, the high molecular weight charge transfer substancesinclude, for example, poly-N-vinylcarbazole, poly-N-vinylcarbazolehalide, polyvinyl pyrene, polyvinylanthracene, polyvinylacridine, apyrene-formaldehyde resin, an ethylcarbazole-formaldehyde resin, atriphenylmethane polymer and polysilane. Of these, the triphenylaminecompound, the triphenylmethane compound and the benzidine compound arepreferred in terms of mobility, stability and transparency to light.

As the binding resin, a high molecular weight polymer which can form anelectrical insulating film is preferred. For example, when the polyvinylacetal resin, the polyamide resin, the cellulose resin, the phenolresin, etc., which are the resins soluble in the alcoholic solvents, areused, the binding resins used together with these resins include apolycarbonate, a polyester, a methacrylic resin, an acrylic resin,polyvinyl chloride, polyvinylidene chloride, polystyrene, polyvinylacetate, a styrene-butadiene copolymer, a vinylidenechloride-acrylonitrile copolymer, a vinyl chloride-vinyl acetatecopolymer, vinyl chloride-vinyl acetate-maleic anhydride copolymer, asilicone resin, a silicone-alkyd resin, a phenol-formaldehyde resin, astyrene-alkyd resin, poly-N-vinylcarbazole, polyvinyl butyral, polyvinylformal, a polysulfone, casein, gelatin, polyvinyl alcohol, a phenolresin, a polyamide, carboxymethyl cellulose, a vinylidene chloride-basedpolymer latex and a polyurethane. Of the above-mentioned high molecularweight polymers, the polycarbonate, the polyester, the methacrylic resinand the acrylic resin are preferred, because they are excellent incompatibility with the charge transfer substance, solubility in thesolvent and strength.

The charge transfer layer 14 may further contain an additive such as aplasticizer, a surface modifier, an antioxidant or an agent forpreventing deterioration by light.

The protective layer 15 contains the resin soluble in the liquidcomponent in the coating solution used for formation of the protectivelayer, the product of hydrolysis and condensation of a mixture of atleast one silicon-containing hole transport compound and at least onearomatic silicon-containing compound. The protective layer 15 mayfurther contain a lubricant or fine particles of a silicone oil or afluorine material, which can also improve lubricity and strength.Preferred examples of the lubricants include the above-mentionedfluorine-based silane coupling agents. In embodiments, the thickness ofthe protective layer is from 0.1 to 10 μm, from 0.5 to 7 μm, or from 1.5to 3.5 μm.

Image Forming Apparatus and Process Cartridge

FIG. 2 is a schematic view showing an embodiment of an image formingapparatus. In the apparatus shown in FIG. 2, the electrophotographicphotoreceptor 1 constituted as shown in FIG. 1 is supported by a support9, and rotatable at a specified rotational speed in the directionindicated by the arrow, centered on the support 9. A contact chargingdevice 2, an exposure device 3, a developing device 4, a transfer device5 and a cleaning unit 7 are arranged in this order along the rotationaldirection of the electrophotographic photoreceptor 1. Further, thisexemplary apparatus is equipped with an image fixing device 6, and amedium P to which a toner image is to be transferred is conveyed to theimage fixing device 6 through the transfer device 5.

The contact charging device 2 has a roller-shaped contact chargingmember. The contact charging member is arranged so that it comes intocontact with a surface of the photoreceptor 1, and a voltage is applied,thereby being able to give a specified potential to the surface of thephotoreceptor 1. In embodiments, a contact charging member may be formedfrom a metal such as aluminum, iron or copper, a conductive polymermaterial such as a polyacetylene, a polypyrrole or a polythiophene, or adispersion of fine particles of carbon black, copper iodide, silveriodide, zinc sulfide, silicon carbide, a metal oxide or the like in anelastomer material such as polyurethane rubber, silicone rubber,epichlorohydrin rubber, ethylene-propylene rubber, acrylic rubber,fluororubber, styrene-butadiene rubber or butadiene rubber. Non-limitingexamples of metal oxides that may be used in embodiments include ZnO,SnO₂, TiO₂, In₂O₃, MoO₃ and complex oxides thereof. Further, aperchlorate may be added to the elastomer material to impartconductivity.

Further, a covering layer can also be provided on a surface of thecontact charging member of embodiments. Non-limiting examples ofmaterials that may be used in embodiments for forming a covering layerinclude N-alkoxy-methylated nylon, cellulose resins, vinylpyridineresins, phenol resins, polyurethanes, polyvinyl butyrals, melamines andmixtures thereof. Furthermore, emulsion resin materials such as acrylicresin emulsions, polyester resin emulsions or polyurethanes, may beused. In order to further adjust resistivity, conductive agent particlesmay be dispersed in these resins, and in order to prevent deterioration,an antioxidant can also be added thereto. Further, in order to improvefilm forming properties in forming the covering layer, a leveling agentor a surfactant may be added to the emulsion resin in embodiments of theinvention.

The resistance of the contact charging member of embodiments may be from10⁰ to 10¹⁴ Ωcm, and from 10² to 10¹² ΩCM When a voltage is applied tothis contact charging member, either a DC voltage or an AC voltage canbe used as the applied voltage. Further, a superimposed voltage of a DCvoltage and an AC voltage can also be used.

In the exemplary apparatus shown in FIG. 2, the contact charging memberof the contact charging device 2 is in the shape of a roller. However,such a contact charging member may be in the shape of a blade, a belt, abrush or the like.

Further, in embodiments an optical device that can perform desiredimagewise exposure to a surface of the electrophotographic photoreceptor1 with a light source such as a semiconductor laser, an LED (lightemitting diode) or a liquid crystal shutter, may be used as the exposuredevice 3.

Furthermore, a known developing device using a normal or reversaldeveloping agent of a one-component system, a two-component system orthe like may be used in embodiments as the developing device 4. There isno particular limitation on toners that may be used in embodiments.

Contact type transfer charging devices using a belt, a roller, a film, arubber blade or the like, or a scorotron transfer charger or a corotrontransfer charger utilizing corona discharge may be employed as thetransfer device 5, in various embodiments.

Further, in embodiments, the cleaning device 7 may be a device forremoving a remaining toner adhered to the surface of theelectrophotographic photoreceptor 1 after a transfer step, and theelectrophotographic photoreceptor 1 repeatedly subjected to theabove-mentioned image formation process may be cleaned thereby. Inembodiments, the cleaning device 7 may be a cleaning blade, a cleaningbrush, a cleaning roll or the like. Materials for the cleaning bladeinclude urethane rubber, neoprene rubber and silicone rubber.

In the exemplary image forming device shown in FIG. 2, the respectivesteps of charging, exposure, development, transfer and cleaning areconducted in turn in the rotation step of the electrophotographicphotoreceptor 1, thereby repeatedly performing image formation. Theelectrophotographic photoreceptor 1 may be provided with specifiedsilicon compound-containing layers and photosensitive layers thatsatisfy equation (1), as described above, and thus photoreceptors havingexcellent discharge gas resistance, mechanical strength, scratchresistance, particle dispersibility, etc., may be provided. Accordingly,even in embodiments in which the photoreceptor is used together with thecontact charging device or the cleaning blade, or further with sphericaltoner obtained by chemical polymerization, good image quality can beobtained without the occurrence of image defects such as fogging. Thatis, embodiments provide image forming apparatuses that can stablyprovide good image quality for a long period of time is realized.

FIG. 3 is a cross sectional view showing another exemplary embodiment ofan image forming apparatus. The image forming apparatus 220 shown inFIG. 3 is an image forming apparatus of an intermediate transfer system,and four electrophotographic photoreceptors 401 a to 401 d are arrangedin parallel with each other along an intermediate transfer belt 409 in ahousing 400.

Here, the electrophotographic photoreceptors 401 a to 401 d carried bythe image forming apparatus 220 are each the electrophotographicphotoreceptors of the invention. Each of the electrophotographicphotoreceptors 401 a to 401 d may rotate in a predetermined direction(counterclockwise on the sheet of FIG. 3), and charging rolls 402 a to402 d, developing device 404 a to 404 d, primary transfer rolls 410 a to410 d and cleaning blades 415 a to 415 d are each arranged along therotational direction thereof. In each of the developing device 404 a to404 d, four-color toners of yellow (Y), magenta (M), cyan (C) and black(B) contained in toner cartridges 405 a to 405 d can be supplied, andthe primary transfer rolls 410 a to 410 d are each brought into abuttingcontact with the electrophotographic photoreceptors 401 a to 401 dthrough an intermediate transfer belt 409.

Further, a laser light source (exposure unit) 403 is arranged at aspecified position in the housing 400, and it is possible to irradiatesurfaces of the electrophotographic photoreceptors 401 a to 401 d aftercharging with laser light emitted from the laser light source 403. Thisperforms the respective steps of charging, exposure, development,primary transfer and cleaning in turn in the rotation step of theelectrophotographic photoreceptors 401 a to 401 d, and toner images ofthe respective colors are transferred onto the intermediate transferbelt 409, one over the other.

The intermediate transfer belt 409 is supported with a driving roll 406,a backup roll 408 and a tension roll 407 at a specified tension, androtatable by the rotation of these rolls without the occurrence ofdeflection. Further, a secondary transfer roll 413 is arranged so thatit is brought into abutting contact with the backup roll 408 through theintermediate transfer belt 409. The intermediate transfer belt 409 whichhas passed between the backup roll 408 and the secondary transfer roll413 is cleaned up by a cleaning blade 416, and then repeatedly subjectedto the subsequent image formation process.

Further, a tray (tray for a medium to which a toner image is to betransferred) 411 is provided at a specified position in the housing 400.The medium to which the toner image is to be transferred (such as paper)in the tray 411 is conveyed in turn between the intermediate transferbelt 409 and the secondary transfer roll 413, and further between twofixing rolls 414 brought into abutting contact with each other, with aconveying roll 412, and then delivered out of the housing 400.

According to the exemplary image forming apparatus 220 shown in FIG. 3,the use of electrophotographic photoreceptors of embodiments of theinvention as electrophotographic photoreceptors 401 a to 401 d mayachieve discharge gas resistance, mechanical strength, scratchresistance, etc. on a sufficiently high level in the image formationprocess of each of the electrophotographic photoreceptors 401 a to 401d. Accordingly, even when the photoreceptors are used together with thecontact charging devices or the cleaning blades, or further with thespherical toner obtained by chemical polymerization, good image qualitycan be obtained without the occurrence of image defects such as fogging.Therefore, also according to the image forming apparatus for color imageformation using the intermediate transfer body, such as this embodiment,the image forming apparatus which can stably provide good image qualityfor a long period of time is realized.

The invention should not be construed as being limited to theabove-mentioned embodiments. For example, each apparatus shown in FIG. 2or 3 may be equipped with a process cartridge comprising theelectrophotographic photoreceptor 1 (or the electrophotographicphotoreceptors 401 a to 401 d) and charging device 2 (or the chargingdevices 402 a to 402 d). The use of such a process cartridge allowsmaintenance to be performed more simply and easily.

Further, in embodiments, when a charging device of the non-contactcharging system such as a corotron charger is used in place of thecontact charging device 2 (or the contact charging devices 402 a to 402d), sufficiently good image quality can be obtained.

Furthermore, in the embodiment of an apparatus that is shown in FIG. 2,a toner image formed on the surface of the electrophotographicphotoreceptor 1 is directly transferred to the medium P to which thetoner image is to be transferred. However, the image forming apparatusof the invention may be further provided with an intermediate transferbody. This makes it possible to transfer the toner image from theintermediate transfer body to the medium P to which the toner image isto be transferred, after the toner image on the surface of theelectrophotographic photoreceptor 1 has been transferred to theintermediate transfer body. As such an intermediate transfer body, therecan be used one having a structure in which an elastic layer containinga rubber, an elastomer, a resin or the like and at least one coveringlayer are laminated on a conductive support.

Examples are set forth hereinbelow and are illustrative of embodimentsof the present invention. It will be apparent, however, that theinvention can be practiced with many types of compositions and can havemany different uses in accordance with the disclosure above and aspointed out hereinafter.

EXAMPLES Examples 1-9

An aromatic silicon-containing compound is prepared having the structureof formula (I), where X is —O—, L is —C₃H₆—, the (RO)_(3-n)R_(n)Si—groups are (^(i)PrO)₂MeSi—, and Ar is one of formulas (II-1) to (II-44).In the following Examples, the aromatic silicon-containing compound isprepared having the structure of formula as defined herein are referredto as compounds (I-#), where # refers to the respective compounds II.Thus, compound (I-1) is a compound of formula I as defined herein, whereAr is formula (II-1).

Example 1 Synthesis of the Aromatic Silicon-Containing Compound (I-1)

Bisphenol A (BPA) (22.83 g) was dissolved in isopropanol (130 mL) in a500 mL round-bottomed flask. To the solution was added a solution of 20wt % of potassium isopropoxide in isopropanol (98.19 g) through adropping funnel. After addition, the solution was stirred at roomtemperature for 3 hours and the excess isopropanol was removed by rotaryevaporation. The remaining solid was dissolved in dimethylformamide(DMF) (360 mL). To the solution was addediodopropyldiisoproxymethylsilane (72.66 g) and the temperature wasmaintained at about 70° C. for an hour, then cooled to 25° C. Potassiumiodide (60 g) was added into the solution and it was stirred for aboutan hour. Cyclohexane (300 mL) was added to extract the product. Thecyclohexane layer was collected and washed with deionized water andbrine, and dried over sodium sulfate. The excess cyclohexane was removedby rotary evaporation and the final product was purified by distillationat 220° C. under reduced pressure. The yield of compound (I-1) was 48 g(75.8%). The desired structure of the product was confirmed by ¹H NMRspectroscopy.

Example 2 Synthesis of the Aromatic Silicon-Containing Compound (I-2)

4,4′-(Hexafluoroisoproylidene)diphenol (25 g) was dissolved inisopropanol (100 mL) in a 500 mL round-bottomed flask. To the solutionwas added a solution of 20 wt % of potassium isopropoxide in isopropanol(73 g) through a dropping funnel. After addition, the solution wasstirred at room temperature for 3 hours and the excess isopropanol wasremoved by rotary evaporation. The remaining solid was dissolved indimethylformamide (DMF) (250 mL). To the solution was addediodopropyldiisoproxymethylsilane (54 g) and the temperature wasmaintained at about 70° C. for an hour, then cooled to 25° C. Potassiumiodide (40 g) was added into the solution and it was stirred for aboutan hour. Cyclohexane (200 mL) was added to extract the product. Thecyclohexane layer was collected and washed with deionized water andbrine, and dried over sodium sulfate. The excess cyclohexane was removedby rotary evaporation and the final product was purified by distillationat 220° C. under reduced pressure. The yield of compound (I-2) was 40 g(72.6%). The desired structure of the product was confirmed by ¹H NMRspectroscopy.

Example 3 Synthesis of the Aromatic Silicon-Containing Compound (I-4)

4,4′-diphenol (9.3 g) was dissolved in isopropanol (50 mL) in a 500 mLround-bottomed flask. To the solution was added a solution of 20 wt % ofpotassium isopropoxide in isopropanol (49 g) through a dropping funnel.After addition, the solution was stirred at room temperature for 3 hoursand the excess isopropanol was removed by rotary evaporation. Theremaining solid was dissolved in dimethylformamide (DMF) (100 mL). Tothe solution was added iodopropyldiisoproxymethylsilane (36.3 g) and thetemperature was maintained at about 70° C. for an hour, then cooled to25° C. Potassium iodide (20 g) was added into the solution and it wasstirred for about an hour. Cyclohexane (200 mL) was added to extract theproduct. The cyclohexane layer was collected and washed with deionizedwater and brine, and dried over sodium sulfate. The excess cyclohexanewas removed by rotary evaporation and the final product was purified byrecrystallization in isopropanol. The yield of compound (I-4) was 17 g(57.5%). The desired structure of the product was confirmed by ¹H NMRspectroscopy.

Example 4 Synthesis of the Aromatic Silicon-Containing Compound (I-5)

Bisphenol Z (26.84 g) was dissolved in isopropanol (100 mL) in a 500 mLround-bottomed flask. To the solution was added a solution of 20 wt % ofpotassium isopropoxide in isopropanol (98.2 g) through a droppingfunnel. After addition, the solution was stirred at room temperature for3 hours and the excess isopropanol was removed by rotary evaporation.The remaining solid was dissolved in dimethylformamide (DMF) (250 mL).To the solution was added iodopropyldiisoproxymethylsilane (72.7 g) andthe temperature was maintained at about 70° C. for an hour, then cooledto 25° C. Potassium iodide (40 g) was added into the solution and it wasstirred for about an hour. Cyclohexane (300 mL) was added to extract theproduct. The cyclohexane layer was collected and washed with deionizedwater and brine, and dried over sodium sulfate. The excess cyclohexanewas removed by rotary evaporation and the final product was purified bydistillation under reduced pressure. The yield of compound (I-5) was49.5 g (73.5%). The desired structure of the product was confirmed by ¹HNMR spectroscopy.

Example 5 Synthesis of the Aromatic Silicon-Containing Compound (I-6)

4,4-(9-Fluorenylidene)diphenol (17.5 g, mole) was dissolved inisopropanol (70 mL) in a 250 mL round-bottomed flask. To the solutionwas added a solution of 20 wt % of potassium isopropoxide in isopropanol(49 g) through a dropping funnel. After addition, the solution wasstirred at room temperature for 3 hours and the excess isopropanol wasremoved by rotary evaporation. The remaining solid was dissolved indimethylformamide (DMF) (mL). To the solution was addediodopropyldiisoproxymethylsilane (36 g) and the temperature wasmaintained at about 70° C. for an hour, then cooled to 25° C. Potassiumiodide (30 g) was added into the solution and it was stirred for aboutan hour. Cyclohexane (200 mL) was added to extract the product. Thecyclohexane layer was collected and washed with deionized water andbrine, and dried over sodium sulfate. The excess cyclohexane was removedby rotary evaporation and the final product was purified by distillationunder reduced pressure. The yield of compound (I-6) was 28.2 g (75%).The desired structure of the product was confirmed by ¹H NMRspectroscopy.

Example 6 Synthesis of the Aromatic Silicon-Containing Compound (I-7)

Hydroquinone (5.5 g, mole) was dissolved in isopropanol (50 mL) in a 250mL round-bottomed flask. To the solution was added a solution of 20 wt %of potassium isopropoxide in isopropanol (49 g) through a droppingfunnel. After addition, the solution was stirred at room temperature for3 hours and the excess isopropanol was removed by rotary evaporation.The remaining solid was dissolved in dimethylformamide (DMF) (100 mL).To the solution was added iodopropyldiisoproxymethylsilane (36.3 g) andthe temperature was maintained at about 70° C. for an hour, then cooledto 25° C. Potassium iodide (20 g) was added into the solution and it wasstirred for about an hour. Cyclohexane (mL) was added to extract theproduct. The cyclohexane layer was collected and washed with deionizedwater and brine, and dried over sodium sulfate. The excess cyclohexanewas removed by rotary evaporation and the final product was purified bydistillation under reduced pressure. The yield of compound (I-7) was15.5 g (60%). The desired structure of the product was confirmed by ¹HNMR spectroscopy.

Example 7 Synthesis of the Aromatic Silicon-Containing Compound (I-13)

1,1,1-tris(4-hydroxyphenyl)ethane (30.6 g) was dissolved in isopropanol(100 mL) in a 500 mL round-bottomed flask. To the solution was added asolution of 20 wt % of potassium isopropoxide in isopropanol (147 g)through a dropping funnel. After addition, the solution was stirred atroom temperature for 3 hours and the excess isopropanol was removed byrotary evaporation. The remaining solid was dissolved indimethylformamide (DMF) (200 mL). To the solution was addediodopropyldiisoproxymethylsilane (109 g) and the temperature wasmaintained at about 70° C. for an hour, then cooled to 25° C. Potassiumiodide (50 g) was added into the solution and it was stirred for aboutan hour. Cyclohexane (300 mL) was added to extract the product. Thecyclohexane layer was collected and washed with deionized water andbrine, and dried over sodium sulfate. The excess cyclohexane was removedby rotary evaporation and the final product was purified by a shortflash column. The yield of compound (I-13) was 65 g (71%). The desiredstructure of the product was confirmed by ¹H NMR spectroscopy.

Example 8 Synthesis of the Aromatic Silicon-Containing Compound (I-33)

Bisphenol P (34.6 g, mole) was dissolved in isopropanol (100 mL) in a500 mL round-bottomed flask. To the solution was added a solution of 20wt % of potassium isopropoxide in isopropanol (98 g) through a droppingfunnel. After addition, the solution was stirred at room temperature for3 hours and the excess isopropanol was removed by rotary evaporation.The remaining solid was dissolved in dimethylformamide (DMF) (150 mL).To the solution was added iodopropyldiisoproxymethylsilane (72.7 g) andthe temperature was maintained at about 70° C. for an hour, then cooledto 25° C. Potassium iodide (25 g) was added into the solution and it wasstirred for about an hour. Cyclohexane (250 mL) was added to extract theproduct. The cyclohexane layer was collected and washed with deionizedwater and brine, and dried over sodium sulfate. The excess cyclohexanewas removed by rotary evaporation and the final product was purified bya flash column. The yield of compound (I-33) was 48.2 g (70%). Thedesired structure of the product was confirmed by ¹H NMR spectroscopy.

Example 9 Synthesis of the Aromatic Silicon-Containing Compound (I-34)

Bisphenol M (34.6 g, mole) was dissolved in isopropanol (100 mL) in a500 mL round-bottomed flask. To the solution was added a solution of 20wt % of potassium isopropoxide in isopropanol (98 g) through a droppingfunnel. After addition, the solution was stirred at room temperature for3 hours and the excess isopropanol was removed by rotary evaporation.The remaining solid was dissolved in dimethylformamide (DMF) (150 mL).To the solution was added iodopropyldiisoproxymethylsilane (72.7 g) andthe temperature was maintained at about 70° C. for an hour, then cooledto 25° C. Potassium iodide (25 g) was added into the solution and it wasstirred for about an hour. Cyclohexane (250 mL) was added to extract theproduct. The cyclohexane layer was collected and washed with deionizedwater and brine, and dried over sodium sulfate. The excess cyclohexanewas removed by rotary evaporation and the final product was purified bya flash column. The yield of compound (I-34) was 50 g (72%). The desiredstructure of the product was confirmed by ¹H NMR spectroscopy.

Comparative Example 1

A conventional crosslinked siloxane-containing overcoat is prepared,i.e., without the aromatic silicon-containing compound.

Specifically, 11 parts of a hole transport molecule (III-1), 5.8 partsof binder material 1,6-bis(dimethoxymethylsilyl)-hexane, 1 part ofhexamethylcyclotrisilane and 11 parts of methanol are mixed, and 2 partsof an ion exchange resin (AMBERLIST H15) are added thereto, followed bystirring for 2 hours. Furthermore, 32 parts of butanol and 4.92 parts ofdistilled water are added to this mixture, followed by stirring at roomtemperature for 30 minutes. Then, the resulting mixture is filtered toremove the ion exchange resin, and 0.180 parts of aluminumtrisacetylacetonate (Al(AcAc)₃), 0.180 parts of acetylacetone (AcAc), 2parts of a polyvinyl butyral resin (trade name: S-LEC KW-1, manufacturedby Sekisui Chemical Co., Ltd.), 0.0180 parts of butylated-hydroxytoluene(BHT) and 0.261 parts of a hindered phenol antioxidant (IRGANOX 1010)are added to a filtrate obtained, and thoroughly dissolved therein for 2hours to obtain a coating solution for a protective layer.

This coating solution is applied onto a charge transfer layer by dipcoating (coating speed: about 170 mm/min), and dried by heating at 130°C. for one hour to form the protective layer having a film thickness of3 μm, thereby obtaining a desired electrophotographic photoreceptor.

Examples 10-14

Crosslinked siloxane-containing outmost protective layers are preparedincluding an aromatic silicon-containing compound of formula (I).Specifically, the procedures of Comparative Example 1 are repeated,except that the aromatic silicon-containing compound of Examples 1, 2,5, 6, and 7 are included. Specifically, the formulation and procedureare the same as Comparative Example 1 except the binder material1,6-bis(dimethoxymethylsilyl)-hexane was changed to the aromaticsilicon-containing compound (I-1), (I-2), (I-5), (I-6), and (I-13).

This coating solution is applied onto a photoreceptor with the samecoating technique and parameters as described in Comparative Example 1.

The photoreceptors prepared in Comparative Example 1 and Examples 10-14are tested for photoreceptor device evaluation. Specifically, thephotoreceptors are tested for their electrical characteristics (V_(high)and V_(low)), wear rate, and deletion resistance.

The electrical evaluation and wear testing and printing test ofphotoreceptors are performed by the following procedure:

The xerographic electrical properties of the above preparedphotoconductive imaging member and other similar members can bedetermined by known means, including electrostatically charging thesurfaces thereof with a corona discharge source until the surfacepotentials, as measured by a capacitively coupled probe attached to anelectrometer, attained an initial value Vo of about −800 volts. Afterresting for 0.5 second in the dark, the charged members attained asurface potential of Vddp, dark development potential. Each member wasthen exposed to light from a filtered Xenon lamp thereby inducing aphotodischarge which resulted in a reduction of surface potential to aVbg value, background potential. The percent of photodischarge wascalculated as 100×(Vddp−Vbg)/Vddp. The desired wavelength and energy ofthe exposed light was determined by the type of filters placed in frontof the lamp. The monochromatic light photosensitivity was determinedusing a narrow band-pass filter. The photosensitivity of the imagingmember is usually provided in terms of the amount of exposure energy inergs/cm², designated as E_(1/2), required to achieve 50 percentphotodischarge from Vddp to half of its initial value. The higher thephotosensitivity, the smaller is the E_(1/2) value. The E_(7/8) valuecorresponds to the exposure energy required to achieve ⅞ photodischargefrom Vddp. The device was finally exposed to an erase lamp ofappropriate light intensity and any residual potential (Vresidual) wasmeasured. The imaging members were tested with an monochromatic lightexposure at a wavelength of 780+/−10 nanometers and an erase light withthe wavelength of 600 to 800 nanometers and intensity of 200 ergs.cm².

The devices were then mounted on a wear test fixture to determine themechanical wear characteristics of each device. Photoreceptor wear wasdetermined by the change in thickness of the photoreceptor before andafter the wear test. The thickness was measured, using a permascope atone-inch intervals from the top edge of the coating along its lengthusing a permascope, ECT-100. All of the recorded thickness values areaveraged to obtain the average thickness of the entire photoreceptordevice. For the wear test the photoreceptor was wrapped around a drumand rotated at a speed of 140 rpm. A polymeric cleaning blade is broughtinto contact with the photoreceptor at an angle of 20 degrees and aforce of approximately 60-80 grams/cm. Single component toner istrickled on the photoreceptor at rate of 200 mg/min. The drum is rotatedfor 150 kcycle during a single test. The wear rate is equal to thechange in thickness before and after the wear test divided by the # ofkcycles.

Immediately after electrical cycling, the electrophotographicphotoreceptors of each of Examples 10-14 and Comparative Examples 1 wereplaced in a xerographic customer replacable unit (CRU), as is used in aDOCUCOLOR 1632 (manufactured by Xerox Corporation) and placed in such amachine for print testing.

Then, print tests were carried out on each photoreceptor. The tests werecarried out under the same conditions of high temperature and highhumidity (28° C. and 85% relative humidity), and the initial imagequality and surface state of the electrophotographic photoreceptors andthe image quality and surface state of the electrophotographicphotoreceptors after 5,000 prints were determined.

The results show that all of the photoreceptors exhibit comparableelectrical characteristics and wear rate, but the photoreceptors ofExamples 10-14 exhibit significant improvement in image deletionresistance due to increased reduced elastic modulus and cleanability ascompared to the photoreceptor of Comparative Example 1 (Table 2). TABLE2 Reduced Image quality Image quality Elastic (initial) (after 5,000prints) Modulus (GPA) cleanability Good medium poor Good medium poorComparative 3.00 ± 0.15 poor ✓ ✓ Example 1 Example 10 3.31 ± 0.14 good ✓✓ Example 11 3.56 ± 0.08 good ✓ ✓ Example 12 3.43 ± 0.09 good ✓ ✓Example 13 3.77 ± 0.17 good ✓ ✓ Example 14 n/a good ✓ ✓

While this invention has been described in conjunction with theembodiments set forth above, it is evident that many alternatives,modifications and variations will be apparent to those skilled in theart. Accordingly, the embodiments of the invention set forth aboveintended to be illustrative and not limiting. Various changes may bemade without departing from the spirit and the scope of the invention asdefined in the following claims.

1. An aromatic silicon-containing compound, having the formula (I):Ar-[X-L-SiR_(n)(OR′)_(3-n)]_(m)  (I) wherein: Ar represents an aromaticgroup; X represents a divalent or trivalent group; L represents adivalent linking group; R represents a hydrogen atom, an alkyl group oran aryl group; R′ represents an alkyl group having 1 to 5 carbon atoms;n is an integer of from 0 to 2; and m is an integer of from 1 to
 5. 2.The aromatic silicon-containing compound of claim 1, wherein saidsilicon-containing compound is selected from the group consisting of


3. The aromatic silicon-containing compound of claim 1, wherein L is adivalent hydrocarbyl group having from 1 to about 15 carbon atoms, andoptionally further contains a heteroatom selected from the groupconsisting of oxygen, surfer, silicon, and nitrogen.
 4. The aromaticsilicon-containing compound of claim 1, wherein R and R′ individuallyrepresents an alkyl group having 1 to 5 carbon atoms.
 5. The aromaticsilicon-containing compound of claim 1, wherein Ar is selected from thegroup consisting of the following compounds (II-1) to (II-44):


6. An outmost protective layer for a substrate, comprising a hydrolysisand condensation product of at least one aromatic silicon-containingcompound of claim
 1. 7. An electrophotographic photoreceptor comprising:a charge generating layer, a charge transport layer, and an outmostprotective layer comprising a crosslinked siloxane composition, whereinsaid crosslinked siloxane composition is a product of the hydrolysis andcondensation of at least one aromatic silicon-containing compound ofclaim
 1. 8. The electrophotographic photoreceptor of claim 7, whereinsaid outmost protective layer further contains a hole transportcomponent of formula (IV):

wherein Ar¹, Ar², Ar³ and Ar⁴ each independently represents asubstituted or unsubstituted aryl group, Ar⁵ represents a substituted orunsubstituted aryl or arylene group, and k represents 0 or
 1. 9. Theelectrophotographic photoreceptor of claim 7, wherein said crosslinkedsiloxane composition is a product of the hydrolysis and condensation ofthe at least one aromatic silicon-containing compound and at least onesilicon-containing hole transport molecule selected from a groupconsisting of

wherein S is at least one member selected from the group consisting of:—(CH₂)₂—COO—(CH₂)₃, —Si(O^(i)Pr)₃—(CH₂)₂—COO—(CH₂)₃—SiMe(O^(i)Pr)₂,—(CH₂)₂—COO—(CH₂)₃—SiMe₂(O^(i)Pr) and —COO—(CH₂)₃—Si(O^(i)Pr)₃.
 10. Theelectrophotographic photoreceptor of claim 9, wherein said outmostprotective layer further comprises a polymeric binder resin selectedfrom the group consisting of polyvinyl acetal resins, a polyamide resin,a cellulose resin, a phenol resin, and melamine-formaldehyde resin. 11.The electrophotographic photoreceptor of claim 10, wherein saidpolymeric binder resin is a polyvinylbutyral having a weight averagemolecular weight of from about 1000 to about 100,000.
 12. Theelectrophotographic photoreceptor of claim 9, wherein X is selected fromthe group consisting of


13. The electrophotographic photoreceptor of claim 9, wherein L is analkylene group having from one to about twelve carbon atoms.
 14. Theelectrophotographic photoreceptor of claim 9, wherein R is an alkylgroup having from one to about four carbon atoms, and R′ is an alkylgroup having from one to about five carbon atoms.
 15. Theelectrophotographic photoreceptor of claim 9, wherein Ar is selectedfrom the following compounds:


16. The electrophotographic photoreceptor of claim 9, wherein saidoutmost protective layer contains from about 20% to about 60% of theproduct of hydrolysis and condensation of the silicon-containing holetransport compounds, from about 20% to about 60% of the product ofhydrolysis and condensation of the aromatic silicon-containing compound,and from about 2% to about 15% of polyvinylbutyral resin; wherein thetotal weight of all components is 100%.
 17. A process cartridgecomprising at least one of a developing unit and a cleaning unit, andthe electrophotographic photoreceptor of claim
 9. 18. An image formingapparatus comprising: at least one charging unit, at least one exposingunit, at least one developing unit, a transfer unit, a cleaning unit,and the electrophotographic photoreceptor of claim
 9. 19. The imageforming apparatus of claim 18, wherein the transfer unit is anintermediate transfer body for temporarily transferring a toner imageformed on the electrophotographic photoreceptor.
 20. The image formingapparatus of claim 19, comprising a plurality of electrophotographicphotoreceptors arranged along the intermediate transfer body.
 21. Amethod of producing an electrophotographic photoreceptor comprising:providing a substrate; forming an underlayer on said substrate; forminga charge generation layer over the underlayer; forming a charge transferlayer over the charge generation layer; and forming an outmostprotective layer over the charge transfer layer; wherein the outmostprotective layer comprises the product of the hydrolysis andcondensation of the aromatic silicon-containing compound of claim 1.